Many mobile transmission systems use power amplifiers for amplifying radio-frequency signals to be emitted. In this case, depending on various external and internal influencing variables it may be necessary to control the output power of the amplifier used. By way of example, an output power of the amplifier is measured and a corresponding controlled variable of the amplifier is adapted in a manner dependant on the output power.
Furthermore, it may be expedient to operate such power amplifiers in such a way that they have a high efficiency with regard to the required and emitted power. However, this can be problematic in particular for small and medium output powers. By way of example, an internal bias current regulation that reduces the bias current of the amplifier for low input powers is provided for this purpose in some power amplifiers.
However, for a predetermined external regulation with regard to the output power which results for example from a power characteristic of a mobile radio standard such as the Global System for Mobile Communication (GSM) standard, such an internal bias current regulating circuit of the amplifier can influence the regulating parameters of the external power regulation. Under certain circumstances, this can lead to the contravention of a predetermined power mask or even to instability of the power regulating circuit.